title: Identification of mutations in SLC40A1 that affect ferroportin function and phenotype of human ferroportin iron overload.
abstract: OBJECTIVE
  Patients with ferroportin iron overload due to loss-of-function mutations in SLC40A1 have macrophage iron overload, hyperferritinemia, and normal transferrin saturation. In contrast, hepatocellular iron storage, hyperferritinemia, and increased saturation of transferrin are a distinct clinical presentation of ferroportin iron overload that results from SLC40A1 mutations that confer resistance of ferroportin to hepcidin-mediated inactivation.
  
  
  METHODS
  SLC40A1 was sequenced in patients from 2 independent pedigrees affected by hepatic iron overload unrelated to HFE. Functions of the ferroportin variants were tested in vitro.
  
  
  RESULTS
  A patient heterozygous for the variant p.W158C in SLC40A1 presented with macrophage iron overload, hyperferritinemia, and normal transferrin saturation. A patient with hepatocellular iron storage, hyperferritinemia, and increased transferrin saturation was heterozygous for p.H507R. Expression of the p.W158C form of ferroportin in 293T cells resulted in defective trafficking to the plasma membrane and reduced iron export activity; the iron export activity of cells that expressed the p.H507R form of ferroportin did not differ from cells that expressed ferroportin without this mutation. The p.H507R of ferroportin localizes normally to the plasma membrane but is resistant to hepcidin-mediated inactivation. Addition of a synthetic peptide derived from ferroportin without these mutations (amino acids 500-518) decreased the inhibitory activity of hepcidin in cells, whereas a peptide from the same region, with p.H507R, had no effect on hepcidin activity.
  
  
  CONCLUSIONS
  The variant p.W158C in SLC40A1 impairs intracellular trafficking of ferroportin, resulting in reduced iron export. The variant p.H507R does not bind hepcidin in vitro and results in apparent hepcidin resistance.
authors.affiliation: Department of Medicine II, Gastroenterology and Hepatology, Medical University of Innsbruck, Innsbruck, Austria.
authors.forename: Roman
authors.initials: R
authors.lastname: Mayr
authors.forename: William J H
authors.initials: WJ
authors.lastname: Griffiths
authors.forename: Martin
authors.initials: M
authors.lastname: Hermann
authors.forename: Ian
authors.initials: I
authors.lastname: McFarlane
authors.forename: David J
authors.initials: DJ
authors.lastname: Halsall
authors.forename: Armin
authors.initials: A
authors.lastname: Finkenstedt
authors.forename: Andrew
authors.initials: A
authors.lastname: Douds
authors.forename: Susan E
authors.initials: SE
authors.lastname: Davies
authors.forename: Andreas R
authors.initials: AR
authors.lastname: Janecke
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Vogel
authors.forename: Timothy M
authors.initials: TM
authors.lastname: Cox
authors.forename: Heinz
authors.initials: H
authors.lastname: Zoller
mesh_terms: D000328:Adult; D023181:Antimicrobial Cationic Peptides / Q000378:metabolism; D001706:Biopsy; D016022:Case-Control Studies; D027682:Cation Transport Proteins / Q000097:blood / Q000235:genetics* / Q000378:metabolism; D004252:DNA Mutational Analysis; D005293:Ferritins / Q000378:metabolism; D020022:Genetic Predisposition to Disease; D057809:HEK293 Cells; D064451:Hepcidins; D006801:Humans; D007501:Iron / Q000097:blood / Q000378:metabolism*; D019190:Iron Overload / Q000097:blood / Q000235:genetics* / Q000378:metabolism; D008099:Liver / Q000378:metabolism*; D008264:Macrophages / Q000378:metabolism; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D009154:Mutation; D010375:Pedigree; D010641:Phenotype; D021381:Protein Transport; D014162:Transfection; D014168:Transferrin / Q000378:metabolism; D000098742:Ferroportin
chemical_list: D023181:Antimicrobial Cationic Peptides; D027682:Cation Transport Proteins; C578702:HAMP protein, human; D064451:Hepcidins; D014168:Transferrin; D000098742:Ferroportin; D005293:Ferritins; D007501:Iron